Posted
by
Unknown Lamer
on Monday January 09, 2012 @10:25AM
from the would-you-like-some-gpio-with-that dept.

An anonymous reader writes with news from Geek.com on an expansion board for the Raspberry Pi. Quoting: "In the middle of December last year the Raspberry Pi Foundation made a surprising announcement that not only would we see the $25 PC released in 2012, it would also be getting an expansion board ... called the Gertboard, and is being developed by Broadcom employee Gert van Loo in his spare time. When completed, it will allow Raspberry Pi owners to play around with flashing LEDs, electric motors, and a range of different sensors. It effectively takes the $25 Raspberry Pi beyond just being a very cheap PC. There's a video of the Gertboard already working which demonstrates the 12 LEDs being lit up and the board powering an electric motor more than capable of lifting something like your garage door."

They have 13$ arduinos... That said, I prefer a Linux machine that can run python, java, apache and everything and then just talk to some IO library or something to take care of moving motors etc.But that's because I am a software guy....

Certainly makes it a lot simpler for the script kiddies to help you make use of your Pi/Gert, eh?

I'm much more interested in Arduino for blinkenlights. All sorts of gizmos out there to Wifi your video to whatever, like wallwart PCs. And they are no more or less secure than the distro they got running.

Of course, for $25-50, you can cheaply find out you don't care to code securely after all, unless you are already, in which case this is cheap cycles for ya. Wax on...

If you're making more than one device you can go even cheaper if you just buy a bare ATMega328 + a couple of cheap components. Granted, you also need a USB to TTL cable which is another $20 or so, but you only need one of those.

Knock off nokia phone data cable (CR42): $2.68 + free shipping. About $4.00-$20.00 to say 'USB TTL' or want some type of connector. In addition to arduinos I talk to a guruplug with one, an unfortunate POS device that will most assuredly be dumped in favor of a pi.

Model B owners using networking and high-current USB peripherals will require a supply which can source 700mA (many phone chargers meet this requirement). Model A owners with powered USB devices will be able to get away with a much lower current capacity (300mA feels like a reasonable safety margin).

They're using 5v over micro usb. Model-A's 300mA works out to 0.3A*5V = 1.5 watts. Model-B's 700mA is 0.7A*5V=3.5 watts. (I'd go with Model B just to double the ram (256MB) + ethernet.)
While the gp will have to account for the efficiency of their power supply as well, I'm pretty impressed w/the rPi. It looks really cool. Here is a nice nice overview [raspberrypi.org], the power-suppy section links to the parent's "archives/260" reference.

From http://www.raspberrypi.org/archives/260 [raspberrypi.org]
Model B owners using networking and high-current USB peripherals will require a supply which can source 700mA (many phone chargers meet this requirement). Model A owners with powered USB devices will be able to get away with a much lower current capacity (300mA feels like a reasonable safety margin).

Arduino programming language (Processing) is very similar to Python or interpreted C.

No, arduino programming is NOT very similar to python at all. Its not even close.

Arduino's native programming languages are C, C++ (with some limitations), and AVR assembler. That's it. The confusion comes from the fact Arduino purposely attempts to obscufate the fact you are using realatively low level languages behind a nice, high level API. None of these are close to python.

When I first started using Arduinos, it took me a week before I figured out the imaginary "script language" everyone talks about, which I could never seem to find, doesn't actually exist. Its completely imaginary. Its 100% marketing and obscufation for C and C++.

This should be informative. Wiring (that Arduino uses) is just a C++ framework. You can of course use it and pretend you have something "simple", but it's really not, and once you hit a compiler error, you better knew C++.

I got fed up with it too, thats why I started MHVLib, a runtime for AVRs that doesn't try and hide its nature.
My design philosophy is that embedded controllers are low on resources, and the runtime should be as lean as possible.
http://www.makehackvoid.com/project/MHVLib [makehackvoid.com]

Depends on the application. Arduinos make twiddling a few logic-level pins and some other useful interface-to-the-world logic quite simple, which is fantastic for certain applications(Linux devices aren't totally impossible in this regard, there are usually some GPIO pins hiding somewhere, and a 'sound card' is a quite capable ADC/DAC if you can manage to get reasonably non-mangled values out of whatever drivers where almost certainly designed for making noises, not sensory applications...).

You know, to set the value of a GPIO pin on an Arduino you just make a single call to digitalWrite(). To trigger a stepper motor you have to toggle the pin's value, which requires (gasp!) two calls to digitalWrite. The equivalent under Linux involves opening the GPIO device file and making multiple read and write calls. For anyone who's ever run a stepper motor using an Arduino the overhead involved in all that boggles the mind. Really, ease of access to the GPIO pins is the least of your considerations whe

Probably not. The CPU in the Pi is much more powerful than the Arduino.Throw in that the PI has a Keyboard and HDMI out as well and things change a bit. With the Arduino you must have PC to program it. With the Pi you just need the Pi with a keyboard and monitor.So lets say you wanted to make a video game with some custom controllers, the Pi would be a much better solution.If you want to make a small weather station that runs on solar power and talks over ZigBee or even a low power HAM radio link with mors

Will this lead to an automated house. Every device in the house should be communicating with a computer. For instance when on turns on a faucet the computer should know there is a reason for water flow so that if there is water flow without a reason it should be able to shut the flow off. I think there should be a computer in every room as long as it is on a network. They should be able to effectively maintain a house and save more energy than they cost.

My neighbors toilet tank cracked while he was on vacation. Result, tons of damage to the house and months of renovations. Luckily, he was insured. Another neighbour had tenants move out and hook up the old washer incorrectly and experienced similar flooding. Anyway. I really had to wonder. A $5 (retail price most likely produced en masse) could easily have detected that water flow was excessive for that particular unit, and shut off the water within minutes, causing minimum damage. For around $50, you c

I suspect that(while they will probably be of assistance to geeks brewing their own) this will suffer the same fate as all the prior 'automated house' widgetry(a market at which they've been hammering for bloody ages now, with comparatively little success).

Suitably motivated geeks, with some major time and pains, and more money than they initially expected to shell out, will indeed hammer out home automation systems. Fundamentally, home automation is a series of really-not-all-that-ghastly problems in AC wiring, switching, sensors, and logic. It will be utterly non-inter-operable with anything else(save perhaps the geek's cellphone of choice, for which he will build a website/app, and possibly an appliance or two into which he will hack directly. Nothing else.)

Joe User, on the other hand, will discover that specific home automation products(eg. cheap programmable thermostats) can be purchased at any hardware store; but more sophisticated systems either pretty much suck, enough that they are really just starting parts for dedicated geeks(eg. X10), or can be purchased, from an installer, in one big, shiny, expensive, bespoke, proprietary package. It'll start at $10,000, be really slick, and interoperate with absolutely nothing that isn't itself.

The various utility companies attempting to deploy "smart meters" for some combination of PR, easier meter reading, and customer behavior metrics will utterly ignore this, since it doesn't comply with their alphabet soup of semi-open-for-interoperability's-sake-but-not-at-all-talked-about-outside-the-industry-or-intended-for-you-to-know-anything-about wireline and wireless protocols(their status seems rather analogous to the state of various 'standards' in the wireless telco wars. Some of them are just totally proprietary, dreamed up by some company large enough that its service area qualifies as a large scale deployment. Others, GSM-like, are standardized cross-industry things; but are really not intended to be fiddled with by end users.

All in all, no difference:

There will still be nothing resembling manufacturer support for appliances that can report and control intelligently(as opposed to just having an external relay cut them on and off, with the exception of a few horrible manufacturer gimmicks that will probably be badly broken and tied to some manufacturer 'portal'. Geeks will continue to homebrew functional, if slightly rough, systems; and it will still be possible to buy very shiny, tightly integrated, totally proprietary widgets for large buildings and custom installs of various sorts.

What dogs 'the automated house' seems not to be a lack of cheap computing power(wireless and fast CPUs certainly helps; but ASM coded PICs communicating over some primitive serial bus through your house's telephone wiring back in the late 80's could have handled it, with some sort of frontend/master-control widget similar to the x86/DOS based CNC machine control systems that persist to this day. Expensive? Yeah. Doable? Yeah.) It seems to be a combination of limited incremental benefit(power just doesn't cost that much, in many locations, doing it manually works OK, for most tasks, setup is currently complex, many locations charge residential customers the same for on and off peak power, so who cares?), complete lack of anything resembling standardization(minimal standardization of even simple things like remote control switches, never mind any sort of direct intelligence built into appliances that can be exposed. PCs have it, in a somewhat clusterfucked way, with ACPI; and some individual devices, like higher end furnaces, might have a manufacturer specific control panel on an HTTP server somewhere; but everything else is largely silent), and some degree of sinister intent by certain entities(the intentions of the power-rationing, 'consumer-metric'-gathering, and similar 'smart-meter' entities are largely not in your interest...)

It's a pity: If it were a primarily technological problem, technology would have curb-stomped it by now. It isn't.

My last call to a "professional Licensed electrician" got me a fairly reasonable quote of $150 to run a wire from the breaker box through the attic to a new hot-tub installation. Then I asked him to make it 10 gauge instead of 12, and the quote increased to $250, when a box of 10 gauge wire that would make the run only cost about $30 (and the 12 gauge cost about $25).

Now, take these same guys and hand them a drawing that involves more than 3 types of co

I used to be an electrician, but then I took an arrow to the knee. Just kidding, a bone tumor broke off, caused an false aneurism, and doctors played copay ping pong with me for a month. I was left unable to work due to nerve damage.

But before that, I used to work with 14 gauge wire, 12 gauge wire, and 10 gauge wire. It is significantly harder to route 10 gauge wire. Even more so if you already have insulation and drywall up. Perhaps things will be different with the 10 gauge equivalent graphene wire gets mass produced at a reasonable price, but until that day you'll need to accept that electricians will charge you extra for the inconvenience of having to deal with 10 gauge when 12 gauge probably more than met the hot tub's requirements.

My particular hot tub was right at the limit of current and distance where 12ga was "acceptable," rather than pay the $100 premium, I routed the wire myself, so, I well know how stiff it is. In my particular circumstance (big attic, bathroom wall still open, breaker box pretty reasonable to access), it might have been an extra 15 minutes effort to wrestle with the thicker wire.

If the electrician just didn't want the job because he didn't like working with 10 gauge wire, he picked a good way of getting his

I concur. Even stranded #10 hook-up wire is at the limit of what I'm designing my power electronics for; #8 is comparatively unwieldy. Pulling a cable with two solid #10 conductors and probably a #12 grounding conductor is a royal pain I'm sure. I'd charge more too, were I an electrician.

Given that standard Linux is not a realtime system, and that to do anything worthwhile you have to write device drivers because there's no direct access even to gpio, I'd say that comparing it to vxWorks is like apples to trolleys, not even oranges. I looked at realtime linux and it seems to be a mess. There's no single, well supported implementation, it seems, and it looked like it'd be more of a liability, long-term, to depend on it. In the end we went with TwinCat.

On or off, true or false, Arduino or R. Pi, Linux or Windows, PC or Apple. Sheesh! Sometimes techies can be so....binary!:D

I've had a lot of fun tinkering with the Arduino [google.com], but I'm stoked about the Raspberry Pi, too. I've got a few projects in mind where even a netbook would be too big, but an Arduino isn't powerful enough. A BeagleBoard or BeagleBone would work, but since the Raspberry Pi is a third of the price, I'll probably give it a try first.

It IS in production, it just hasn't come out of the production pipeline yet. The working beta boards (with a hand-applied last-minute fix) are being auctioned off, proceeds for the charity recipients for which Raspberry Pi was created: making classroom computing happen.

I will be happy to buy a bunch when they're available too, but let's watch the development. As for Tesla, did you buy the Roadster, seeing as how it's been available in showrooms for some time now?

The pre-production versions are available on eBay now. There only one circuit difference between them and the final model. I think they're in production now but will not be sold until they get a significant inventory built up, about the end of the month.

I'm very excited about this.Especially as a learning tool for my kids, I think that by seeing what is happening they'll get very excited about learning to program.I already have arduino boards, but it's not the same thing. Here we have a completely self-contained computer with great practical I/O interfaces.

It's cheap enough that you can give it to kids without worrying if they break it and the expansion board will let them see and play around with some real world applications without everything being on the screen, dry and abstract.

Actually you make an interesting point.A board like this but that connected to you PC with a USB interface could be very useful.With proper libraries and bindings for things like Python, Perl, Ruby, Lua, C, C++, and so on would be very cool tool for people to play with.Of course one could make such a device from a Pi and even have it be networked. Realtime control would be a challenge but for none realtime control it could be kind of cool.

Who are these people who keep on insisting on using through-hole components? That board could easily be the same size as the Raspberry-pi board itself simply by using SOIC packages as opposed to DIP for all of the ICs. Soldering a 1.27mm pitch SMT component is really easy, it takes about the same amount of time as a DIP component, and is much, much, smaller.

I understand from the Raspberry-pi website that it's gonna be supplied as a bare board + components, but like I said, soldering SMT stuff is really easy. Also if the whole point of this Raspberry-pi stuff is to teach people new skills, why not teach them how to solder stuff that the rest of the world is now using.

Soldering a 1.27mm pitch SMT component is really easy, it takes about the same amount of time as a DIP component, and is much, much, smaller.

No.

Perhaps to a seasoned EE or hobbyist who gets his hands dirty on a daily basis, but otherwise, no.

The best way to turn the Raspberry Pi to shit (apart from its name - "Acorn", the obvious predecessor to this whole project, sounded much better) would be to set the bar at a level which assumes you already know what you're doing before you've even started.

Who are these people who keep on insisting on using through-hole components? That board could easily be the same size as the Raspberry-pi board itself simply by using SOIC packages as opposed to DIP for all of the ICs. Soldering a 1.27mm pitch SMT component is really easy, it takes about the same amount of time as a DIP component, and is much, much, smaller.

Its a meme that just won't die. As a guy who's been doing SMD at home on and off since the 80s for ham radio microwave gear, it gets tiring hearing for about three decades that what I find easy to do and enjoyable is "impossible" and will be the "death of homebrewing" and all that rot. Its right up there with "PL-259s are impossible to install" and "power poles are impossible to install", you only hear about it over and over from the 0.1% of the population who really can't do it.

I'm willing to bet there are some very young hardware hackers on/. right now emulating their elders by rambling about how impossible it is to do SMD at home, despite my experience doing it for years before they were born.

I've soldered plenty of SM components myself, but you may be overlooking the novice oriented aspects of this system (and the comments you dismiss), especially when it comes to the tools available. Besides, practice only takes you so far; even an experienced plastic surgeon may have a hard time making something look pretty if he's only got leather-working tools available.

If you consider that the computer is marketed as cheap, and this board is an educational add on (presumably also cheap) (well the board is functional, but the article points out the educational advantages, including the population), then it would probably be safe to assume that the soldering iron will also be cheap. A soldering iron allowing comfortable SM work is easily double or triple the cost of the computer - over an order of magnitude for the good ones. So, if one were to use a soldering iron of comparable or less cost than the system (what a novice may choose to start with), SM could be very hard if not impossible.

SparkFun sells a temperature-controlled iron perfectly suitable for general SMD work for $40 [sparkfun.com]. Sure, that's more than the cost of the computer, but I suspect it's less than computer + addon board. Yes, a good iron used to cost $150, but that's simple no longer true. (Sure, the $150 iron is somewhat better, but the $40 one can do 1.27mm gull wing packages just fine.)

Would that be the Xytronic [xytronic-usa.com] which sells some really cute soldering irons with identical pictures to those in the catalog of Xytronic [xytronic.com] who states "Ninety percent of XYTRONIC product is exported with major customers in the US, Canada, Australia, Japan and Western Europe"?

Yes you can. Even I can solder SMD with my 15 year old soldering iron. However, soldering through hole is much easier, less error prone and requires simpler tools.

I've seen someone fix an audio system with just a 12V soldering iron in the middle of a field, on a wobbly table. Try that with SMD. Usually I want my stuff to last and to be easy to fix/modify. From a hackers point of view, trough hole is just better. More expensive, but better.

Well the problem with PL-259s are most people have undersized soldering irons. Not to mention there are better connectors out there nowadays anyways.

The killer with PL-259s is/was two fold:

1) I use ladder line and change is too scary to contemplate so I'll use ladder line until I die. Lets face it most of those old timers have kicked the bucket so thats why we're not subjected to as much "pl-259 sucks" as we used to be.

2) The old ham adage that hams make their own antenna wire by grabbing each side of a penny and pulling really hard remains true. You really can't reuse a PL-259. Yeah you can try, but its agony. If its new and shiny and licks up sold

I did all my own tech assembly work when through-hole was the only option. As the years wore on, my eyesight got worse and the parts got smaller, rapidly taking me out of the tech arena - which is fine, but I can still do through hole, whereas mounting an 0402 is... unrealistic for me.

*disclaimer* I work for Broadcom in the team that did 2835, however I am not involved with the Pi, so posted anon to not to be accused of karma-ing

Reasons For through hole:1) Hobbyists aren't scared of them - some are scared of SMT (and some SMT is used on Gertboard)2) Requires less skilled soldering - yes a skilled solderer can do smt with ease, but half the point of this project is that it should be unintimidating to everyone.3) More mechanically sturdy. Useful for many hobby projects

The Pi mainboard got in trouble for being none through-hole, and not available as a kit of parts, now Gertboard is in trouble for being exactly that.*sigh* this is why we can't have nice things.

Soldering a 1.27mm pitch SMT component is really easy, it takes about the same amount of time as a DIP component, and is much, much, smaller.

The thing I find takes the time with SOIC components is getting them aligned and keeping them aligned while I do the first couple of pins (diagonally opposite of coutse). Once you've done that first pin the rest is pretty easy but i've always found the first pin a PITA.

Also another BIG advantage of DIL is that it can be socketed. That means it's much easier to replace a part if you fry it. It also means if a board doesn't work you can pull chips out either to let you test the board itself for shorts etc or to allow you to test sections of the circuit in isolation.

I'll use surface mount if i'm space constrained or can't get the part I need in a DIL package but I much preffer DIL.

"Winging a pin" (removing the pin from the board and connecting to a wire) to change the circui

Pre solder two pads diagonally opposite. Sit the component and align it. The legs on the pre-soldered pads will be sprung up. Touch those two lets with the iron. It will flow the solder and the legs will spring back down into place.

I know, it's great and all, but if you're using the pi to do the heavy lifting, and the gert as simply a way to output, doesn't an arduino already do this, and with linux too? Is this redundant, or have I missed something?

This is more similar to a BeagleBone prototype cape - except with the Gertboard don't expect to be able to use any features in the chip that aren't put into the kernel by Eben and Gert. Unlike the CPU in the Arduino (ATMegaXX8) and the CPU in the BeagleBone (TI AM335x), the technical reference manual for the Broadcom chip in the Pi is completely unavailable. If support for anything is left out of the kernel, whether intentionally or simply due to lack of time, you will not be able to implement it yourself. If support for anything is broken in the kernel, you will have to live with it due to lack of documentation and the fact that Broadcom never comments their damn kernel code for anything. (Look at the BCM4330 driver for mobile devices as an example - if it misbehaves, you're screwed.)

except with the Gertboard don't expect to be able to use any features in the chip that aren't put into the kernel by Eben and Gert.

Except the Gertboard is just using GPIOs are presented as standard file interfaces. You can toggle them with any programming language, shellscript, or just typing 'echo 1 >/sys/class/gpio/gpio1/value' at the CLI.

The GPU may be locked down and worthless for hacking, but the expansion pins are anything but.

As I said, I am not a hardware hacker, so I don't really know what I am talking about, but is there a reason why the ARM1176JZF-Sâ Technical Reference Manual from infocenter.arm.com (sorry, I couldn't find a way how to link to documentation for a particular chip in their system) would not be enough?

http://www.ti.com/product/am3359 [ti.com] - Note the 20MB TRM that is the third PDF linked on this page. This is the sort of documentation TI provides for their products. This is the sort of documentation you need when hardware hacking.

You forgot to mention the bandwidth differences between embedded software on a microprocessor and an OS controlled I/O system. There is a (theoretical) huge performance difference in high speed/response between the two.

And to the AC mentioning competition: these are not really in the same product class. There are probably a large number of applications where the end goal could be achieved with either set of hardware, but there are probably more projects which do not overlap (especially if your concerned w

Arduino does not run linux. You can run the editor / compiler / loader on linux, but its just a bare metal controller.The pi literally runs linux, so you develop on board.

Stereotypically, you'd use something like a gert or a usb connected arduino as the hardware interface. Then you'd simply "apt-get install octave" or whatever on the pi, write a tiny little perl script or whatever to talk to your hardware interface, and write your PID loop or whatever in octave script on the pi. Along with probably runni

Both would be developed on the host linux PC, but Arduino is already rather mature and well supported, and connects via USB with no soldering to your shiny new Raspberry pi. What's the gertboard bringing to the table in addition to what the arduino does already?

Arduino is a computer, not in of itself an I/O peripheral, so if you wanted to do I/O from a Raperberry Pi via an Arduino you'd basically be sending software commands from the Pi to the Arduino then have a program running on the Arduino to do the actual I/O... it's way more efficient just to use a Gertboard and do I/O directly from the Pi.

Compare the two:

Pi + Gertboard - runs at Pi speed (>> Arduino speed), and no need for a seperate I/O program

I can't think of any situation where Pi + Arduino really makes sense. Other than Gertboard for GPIO, using USB peripherals (e.g. servo driver, etc) with Pi makes more sense.

When it inevitably doesn't work, and I need to do the divide and conquer thing, I can attach the Arduino to my desktop linux box and run the exact same code to prove it's not a CPU power thing, or an obscure Pi USB bug, or an obscure Pi bug in general, and/or the heavy desktop has plenty of power and screen realestate to run dumps etc. Also watching/reverse engineering USB signals is very old and well understood so watching how the Arduino and Pi talk to each other should be childs play.

Given a choice, would you want your development environment to be running on such a limited machine? I'm not putting the Pi down, it's great for what it is, but at the the end of the day it's a $25 computer. Anybody who thinks it will compare well to the desktop PC they normally use is deluded.

Good enough for browsing? Because I could see myslelf with one behind this LCD monitor hooked up to the spare HDMI slot. A PC that runs on effectively battery power for when I only need a browser sounds good to me. Saves me having this i7 on all the time. And I'm sure it could download through the night onto an external HDD for very little power overhead.

Anybody who thinks it will compare well to the desktop PC they normally use is deluded.

Oh, of course it will compare well. Hmm so lets consider the stereotypical educational institution lab task of writing a embedded thermostat. This 10 ohm resistor epoxied to this thermistor will be heated up precisely to happy tropical fish temp... This sounds like a very stereotypical embedded lab, I think I did something like this in school back in '93 using a then new motorola microcontroller. This is a very stereotypical "3 hour lab" type of task.

There are some aspects that are redundant but there is a lot more that is not. Here are some major differences:

Arduinos do not run Linux. Their code is written in Assembly, C or C++ but WITHOUT the STL. There is no OS or kernel. It's pure monolithic code running on a Atmel Atmega328, ATmega2560 or similar processor. They support Analog I/O, Digital I/O, I2C, SPI, 1-wire, EEPROM, Serial communication via digital i/o lines or Serial over USB, typical 16Mhz clock speed and 8k of RAM, 32-256K of program storage. It probably uses slightly less power than the Raspberry Pi.

Raspberry Pi do run Linux. Their code is written in any language supported by an ARM 1176JZF-S CPU with a Linux kernel such as Assembly, C, C++ with STL, Python, Perl, etc. There is a OS such as Debian, Arch with more to follow and a Linux kernel. Code written is traditional Linux code running in a multi-tasking system such as Linux provides. It's run on an ARM 1176JZF-S CPU. They support Digital I/O I2C, SPI, Serial communication via digital i/o (gpio) lines, SD card support, composite video out, HDMI video out, RCA audio out. 700Mhz clock speed, 128-256MB of RAM, 1-32GB of program storage (depending of SD card size).

Unlike the Raspberry Pi, the Arduino cannot be developed on by itself. It requires another computer running Linux, OS X or Windows in order to develop on them.

The Gertboard is more akin to what an Arduino shield is for an Arduino. It's just something you plug into a Raspberry Pi to provide access to more of the GPIO pins of the Raspberry Pi's SOC and it has some convenience functionality like LEDs built-in. Like an Arduino shield, it's optional. You can still use GPIO pins on the Raspberry Pi without it.

I looked at the pcb pix and saw the SPI interface lines and incorrectly guessed the whole thing runs off one SPI connection, which would be kind of cool, since pretty much every microcontroller made in the past 30 years is either has SPI hardware support or is at least easy to bit bang SPI. So it would not really be a pi board, but a generic board that works with everything that merely has support to directly plug a pi into it.

However I read the comments and the deal is the breakout board brings 18 GPIO ports from the pi, and you wire the GPIO ports however you want to various peripherals at the GPIO level, one of which is a SPI interface port expander, other things you could wire to are the motor drivers, etc.

So its really a mostly GPIO board with exactly one SPI part, not a board run entirely off just one SPI port. For example, if you have an old fashioned parallel port on your PC, plus or minus some level conversions you could wire that up to this board, etc.

The other interesting comment I read was something similar to "if you want arduino shield support on a pi, simply plug an arduino into the USB port and plug the shield into the arduino and talk to the Ardunino using the linux usb drivers", which is brilliantly simple.

As parallel ports become rarer(if not extinct already), I could see this becoming the best way to control CNC/3d printers once somebody ports a RTOS version of Linux to it.

I have a CNC mill in the basement and your theory is pretty much on track for current applied work.

CNC mills are mostly PCI or motherboard printer port controlled right now, no they are not extinct although endangered species is probably appropriate phrase, and semi-intelligent USB attached controllers have been moving into the market for quite a few years.

The problem with the USB controllers is they are generally not too smart and don't handle lookahead/smoothing as well as printer port and real time PC ba

Arduino and Raspberry Pi are not competators in any way. They target two different markets whereby they have very slight overlap for hobbiests. The Pi simply can not compete with Arduino/AVR on the low end and Arduino/AVR can not compete with RPi on the highend. There's only a tiny intersection between the two and that's likely only because you have one or the other whereby a "close enough" solution is satisfactory.

AVR/Arduino has solutions in the $1-$6 range, if you want to use an inexpensive ISP [ebay.com] and break out the coresponding pins on your bare bones [moderndevice.com] or really bare bones [solarbotics.com] controller. Not to mention, the pins are easy to access with a multitude of more pins available. It also has some capabilities which are simply not available without a Gert board, which makes the pi all the more expensive. Furthermore, an RPi is basically as barebones as you're going to see - at least for a while - if ever. Whereas for the AVR/Arduino solution makes it easy to transplant your Arduino project into a barebones $3-$9 project.

Furthermore, these two projects are really far and away much more complimentary technologies than they are competators. Basically, let the RPi do the heavy CPU lifting and the AVR's do the GPIO and bit flipping. Its a combination made in heaven.

Uuum, I looked at those sites. And all I see is "in the pipeline", "if you have any ideas", "mailing list" and "could potentially be developed as X".There are no ways to order anything, not even a name to call whatever they are doing. Not even pictures.

Either I overlooked something, or this is the king of vaporware and hasn't passed the "Well, we thought it would be cool to have X. But we haven't anything more to offer." stage.

Can you point me to a link where I can put my money and get a Raspberry-Pi-like b